The growth in demand for broadband services has led to increased activity in research and development of high capacity optical systems and networks. It has been predicted that quasi-linear optical communication systems such as Chirped Return-to-Zero (CRZ) and Dispersion Managed Soliton (DMS) systems will play an important role in these future networks.
The capacity of existing standard optical fiber currently installed is far greater than the capacity presently utilized. This capacity potential can, for example, be exploited through use of Wavelength-Division Multiplexing (WDM) in quasi-linear optical systems.
In optical communication systems, the main sources of errors include chromatic dispersion, fiber non-linearities, Polarization Mode Dispersion (PMD), and Amplified Spontaneous Emission (ASE) noise from the amplifiers. In WDM optical communication systems nonlinear interactions of optical pulses among different channels can cause severe inter-channel interference which may be converted into Timing Jitter (TJ) thus effectively decreasing the actual capacity.
Several different approaches such as fiber dispersion management, a jitter-tracking demultiplexer, optical equalization, Forward Error Correction (FEC), and line coding in optical systems have been proposed to combat these impairments. It has been especially shown that dramatic improvements can be obtained in repeater-less undersea systems by the use of FEC. These studies, however, are primarily based on standard FEC and line coding schemes and there has been little effort to optimize the choice of codes and to design new codes which take into account the physical mechanisms behind the impairments. Moreover, while the use of standard line codes has been studied, they have yet to be implemented in commercial systems.